Profitability. Those go carts were probably expensive to maintain, and only being able to run 2-3 carts at a time was reducing the number of people they could make money off for every minute of track usage.
Most people are also IDIOTS when it comes to driving. Just drive down the road at any time and you'll see it. So they are catering to the larger market, the people who don't care about times, but who just want to pretend to be a good driver and run other people off the road and not feel guilty about it. If they posted times, people would get butt-hurt finding out how much they really suck.